ZIL

ZIL
Authoring system
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Interaction style	Parser
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ZIL is short for Zork Implementation Language, a programming language developed by Infocom and based on MDL, which itself is a version of Lisp.

A Brief History

The original pre-Infocom game known either as Dungeon or Zork was written in MDL and could run on a mainframe computer. But the original Zork could not run on typical 80's home computers because of their memory and processor restrictions. Part of the solution, of course, was to split the game into three parts: Zork I, II and III. But more importantly, Infocom created ZIL by removing features of MDL that they didn't need, and by targeting ZIL for a virtual machine that they called the Z-machine.

Because the Z-machine was specifically designed for playing text adventures, the opcodes of its virtual processor could be likewise specifically designed. The opcodes of a Z-machine are called Z-code. The end result was that a game compiled from ZIL produced a story file small enough to fit on an 80's personal computer.

One more thing was needed: an interpreter to emulate the Z-machine. Infocom named their interpreter the Zork Interpreter Program ("ZIP"). A different version of ZIP was required for each computer model (Apple II, Atari, DEC Rainbow, etc.)

Present Day

Even though Infocom's compiler, ZILCH, was thought to be lost, it has been possible to write new games in ZIL ever since ZILF was released in 2010. A version of ZILCH's source code was later recovered and can be run on a PDP-10 emulator.

Interest in ZIL grew after Jason Scott uploaded the source code for many of Infocom's games to GitHub in 2019, and again after Microsoft released Zork I–III as open source in 2025. Although Infocom's compiler, ZILCH, was no longer available, the games could be compiled with ZILF.

In 2023, the first IF Comp entry written in ZIL was submitted: Milliways: the Restaurant at the End of the Universe.

See also

• e-ZIL, the Emacs Z-Machine Interface Language by Marc Simpson. (The e-ZIL project is now dead.)
• ZILF, a modern ZIL compiler.
• Z-machine, the virtual machine that ZIL and Inform compile to.

Links

• ZIL manual (PDF format; 78 pages) — Learning ZIL - or - Everything You Always Wanted to Know About Writing Interactive Fiction But Couldn't Find Anyone Still Working Here to Ask
• ZIL Facebook group
• Explanation of how to run ZILCH on a PDP-10 emulator